Method of refinishing the surfaces of a plastic article



United States Patent 3,443,008 METHOD OF REFINISHING THE SURFACES OF A PLASTIC ARTICLE Walter S. Boyhan, Laurelton, Rudolf Mayer, Roslyn Heights, and Arthur H. Staheli, Seaford, N.Y., assignors to Western Electric Company, Incorpo-- rated, New York, N.Y., a corporation of New York No Drawing. Filed Oct. 23, 1965, Ser. No. 504,207 Int. Cl. 1529c 25/00 US. Cl. 264-341 16 Claims ABSTRACT OF THE DISCLOSURE The surfaces of an acrylonitrile-butadiene-styrene (ABS) article are refinished by penetrating a quantity of solvent through an oxide coating thereon to dissolve a portion of the underlying plastic and thereby remove the oxide coating. An additional quantity of solvent, now containing dissolved plastic, is absorbed into the newly uncovered surfaces which are then dried to evaporate the solvent and to redeposit the dissolved plastic. The article is then heat treated to relieve stress forces developed in the surfaces during drying.

This invention relates to a method of refinishing the surfaces of articles made from plastic and, more particularly, to a method of refinishing, to original specifications, the surfaces of an article made from acrylonitrile-butadiene-styrene copolymer. It is an object of this invention to provide an improved method of such character.

In recent years acrylonitrile-butadicue-styrene (ABS type plastic) has been utilized extensively in injection molding techniques to produce a variety of plastic articles for commercial use. One example of such use is found in the telephone industry wherein the ABS type plastic is utilized to produce the housings, handles and the transmitter and receiver caps of commercial telephone sets in a variety of different colors. Under normal use conditions, the surfaces of such exposed telephone articles are stained and minutely cracked by contact therewith of foreign contaminants such as human perspiration, tobacco smoke and cosmetics. Such surfaces are also marred and scratched by engagement therewith of either blunt or sharp objects. This staining, minute cracking, marring and scratching of the initially high gloss surfaces of such exposed articles leads to a marked deterioration of the physical characteristics of these surfaces and a resulting dulling thereof. As the telephone companies are often required to take back or replace such telephone sets for various reasons, such as subscribers changing residences, or requesting a different type of phone and/or service, refinishing or replacing phones of the type in question has proven very costly.

Heretofore, the deteriorated housings, handles and caps of the telephone sets taken back have been initially inspected to determine which of such articles could be recovered by a surface buffing operation. However, because of both the relatively high cost and degree of difiiculty involved in the bufiing of complex surfaces, a bufiing operation generally has been restricted to those articles which have exhibited only relatively minor deteriorated surfaces or blemishes. The other, more highly deteriorated articles generally have been discarded and replaced with newly molded counterparts inherently exhibiting surfaces with the desired and/or required gloss and physical characteristics.

As substantial expenses have been encountered in either bufiing or having to replace badly deteriorated molded articles utilized in telephone sets heretofore, a definite ice need has thus existed for an economical and eflicient method of refinishing deteriorated surfaces of such articles to original specification.

It is therefore another object of this invention to provide a method of refinishing marred, scratched, cracked and stained surfaces of plastic molded articles made from acrylonitrile-butadiene-styrene copolymer, which method produces on such articles new surfaces having physical characteristics comparable to the physical characteristics obtained on the surfaces in the initial molding of such a copolymer.

It is still another object of this invention to provide a method of refinishing complex, deteriorated surfaces of plastic molded articles made from acrylonitrile-butadienestyrene copolymer in such a manner that the complex surfaces have a refinished high gloss surface theeron which has physical characteristics comparable to the physical characteristics obtained on such surfaces in the original molding of such articles.

It is a further object of this invention to provide a method of refinishing surfaces of articles made from acrylonitrile-butadiene-styrene copolymer, such as telephone housings, handles and caps, which is simple and effective in operation and economical to utilize.

In accordance with one preferred method of this invention, deteriorated surfaces of an article made from an acrylonitrile-butadiene-styrene copolymer, are refinished to original specifications by initially contacting the plastic surfaces to be refinished with an essentially two-stage permeating agent.

In accordance with the principles of this invention, a quantity of the agent, in the first stage, penetrates into such surfaces to a depth effective to cause a removal therefrom of a layer of deteriorated surface plastic such that new surfaces are uncovered. Another quantity of the agent, in the second stage, is absorbed into the uncovered surfaces to a depth effective to cause a partial dissolving of a thin layer of the uncovered surfaces so that a quantity of the agent coating the surfaces contains dissolved plastic.

After the agent contacting operation, the article is dried for a period of time suflicient to allow both an evaporation of the agent coating the surfaces and a redeposition of the dissolved plastic on the surfaces to cause a refinishing thereof. During the period of redeposition, a substantial development of stress forces is produced in the refinished, high gloss surfaces.

To terminate the process, the article is heated to a temperature below the melting point of the plastic for a period of time sufiicient to relieve the stresses developed in the refinished surfaces such that the surfaces have physical characteristics comparable to the physical characteristics obtained on the surfaces in the initial molding of such plastic. In addition to relieving the developed stresses, this heating period additionally serves to remove virtually all of the remaining agent absorbed in the surfaces which would otherwise eventually escape from the plastic and cause a redevelopment of surface stresses.

This invention, together with further objects and advantages thereof, will best be understood by reference to the following detailed description thereof. It should be understood that the method ot be described may be utilized in conjunction with any article made from plastic exhibiting characteristics like or similar to acrylonitrilebutadiene-styrene copolymer, but the following description will be specifically directed to certain molded articles of telephone sets made of the above-mentioned copolymer.

Housings, handles and caps of telephones made from acrylonitrile-butadiene-styrene copolymer are extensively utilized in telephone installations on subscribers premises. During normal use, the surfaces of such articles are slowly oxidized by atmospheric contact therewith. This oxidation is believed to take place at nonreacted carbon double bond sites on the surfaces of the plastic material to cause a resulting cross linking of the extending chain lengths of such a polymerized plastic material. Because of the chemical and physical changes which occur with the oxidation of the plastic material, the surface layer 'of plastic on the exposed telephone articles takes on significantly different chemical and physical characteristics than those which it initially possessed.

Once oxidation has occurred at a particular double bond site, the surface layer of acrylonitrile-butadiene-styrene copolymer is readily attacked by human perspiration, tobacco smoke, cosmetics and the like, to cause a staining and minute cracking of the plastic in the vicinity of the oxidation. The oxidized surfaces of the plastic are also susceptible to being marred and scratched by either blunt or sharp objects which come in contact therewith.

Thus, as an original, high gloss surface of acrylonitrilebutadiene-styrene copolymer is slowly oxidized, staining, cracking, marring and/or scratching thereof will take place. It is for this reason, primarily, that the surfaces of the housings, handles and end caps of telephone sets may deteriorate in appearance over a period of time. The subject method is concerned primarily with the refinishing of such surfaces in an economical and efiicient man ner.

As a desirable preliminary step, but not a necessary step, before practicing the method of this invention, any articles which are to be subjected to the process are preferably washed with detergent, rinsed in water, drained and, if desired, thereafter allowed to dry so that surface dirt is removed therefrom in a standard manner.

In accordance with the principles of this invention, the method is initiated by subjecting the deteriorated surfaces of the articles made from acrylonitrile-butadienestyrene copolymer to a spraying operation wherein a spray of two-stage permeating agent is directed against the surface or surfaces to be refinished. The chemical compositions of the two-stage permeating agents found acceptable for practicing the method of the invention will be described in detail hereinbelow. It will suffice to say at this point that the agent is either a solvent for the plastic or a solution of a strong solvent for the plastic and a diluent or weak solvent for the plastic.

During an initial period or stage of the spraying time, the two-stage permeating agent is effective to penetrate through the outer oxidized deteriorated surface layer of the copolymer article. This causes a thin layer of unoxidized plastic immediately under the deteriorated layer to dissolve completely, resulting in the subsequent spray removing the deteriorated layer and exposing a new outer surface. During a final period or second stage of the spraying time, the agent is effective to penetrate into and be absorbed by the new outer surface or surfaces uncovered by removal of the deteriorated surface layer of plastic. As will be amplified on hereinafter, it is the latter absorbed solvent which ultimately affects the development of a high gloss on such uncovered surface or surfaces.

By way of example, one or more of the following solvents may be used as two-stage permeating agents for the spraying operation: ketones, such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters, such as methyl acetate, ethyl acetate and ethylene glycol monethyl ether acetate; dimethyl formamide; and tetrahydrofurane. However, the most effective solvent for this process has been found to be dichloromethane.

The above listed strong solvents for the ABS type plastic may be diluted to form the permeating agents with one or more of the following diluents: alcohols, such as methanol, ethanol and propanol; others, such as ethyl ether and isopropyl ether; parafiinic and aliphatic hydrocarbons, such as pentane, hexane and heptane; and l,l,l-trichloroethane. However, when dichloromethane is utilized as the strong solvent, the preferred diluent therefore is trichlorotrifiuoroethane.

The two-stage permeating agent found most effective for the refinishing of articles made from an acrylonitrilebutadiene-styrene copolymer consists essentially of to 100% by volume of the strong solvent dichloromethane and 35 to 0% by volume of the diluent trichlorotrifluoroethane. The preferred agent consists essentially of a by volume solution of this strong solvent and the diluent therefor.

In the remaining description of the method of this invention, two examples of the method of this invention will be set forth. One example will disclose the use of the preferred permeating agent of 70% by volume of dichloromethane and 30% by volume of trichlorotrifiuoroethane while the second example will disclose the use of a permeating agent of 50% by volume of dichloromethane and 50% by volume of 1,1,1-trichloroethane. Other twostage permeating agents may be utilized, but when such are used, slight variations in the time periods for particular steps or in temperatures at which the steps are carried out may result. However, in the further description of each of the steps of the method, a complete description will be given of the results to be achieved by that particular step regardless of the solvent or solvent-diluent solution utilized for the spraying composition. With such a description, one skilled in the art will be able to adjust the time and temperature associated with each step so as to facilitate the use of a number of desired solvent or solvent-diluent solutions in accordance with the described method.

The spray operation with the preferred solvent-diluent solution of 70% by volume of dichloromethane and 30% by volume of trichlorotrifiuoroethane may be carried out for a period of 5 to 40 seconds, preferably 10 to 20 seconds, with the temperature of the solvent or solution being maintained at a temperature of 40 to F., preferably 60 to 70 F. When the preferred solution is maintained at a temperature of approximately 65 F., 3 to 5 seconds of spraying time are required to allow sufficient penetration of the spray through the oxidized surface layer of plastic to cause the initial removal thereof.

Significantly, the spray penetrating through the surface layer' of oxidized plastic has been found to loosen and undermine this layer of plastic by attacking and dissolving the fresh plastic therebelow. This physical reaction results in the removal of the deteriorated layer which is swept away by the force of the continued spray of the preferred solution such that a new surface of fresh plastic material is uncovered or exposed.

As soon as the oxidized surface layer of plastic is removed from a particular portion of the article, the solution is absorbed into the newly uncovered surface. The absorbed solution is effective to dissolve further a layer of fresh plastic, a portion of which plastic is redeposited in a later step of the method to produce smoothness and gloss characteristic on the refinished articles which are similar to those found on the surfaces of newly molded articles. In general, only a relatively short portion of the solution spraying period is required initially to remove the outer oxidized layer of plastic, the major portion of the spraying period being employed to direct the solution against the uncovered surface.

Upon termination of the spraying operation, a sprayed article may be subjected to an optio al step wherein the article is maintained in a substantially saturated atmosphere of the vapors of the preferred solution utilized for the spray. The article is held in this atmosphere for a period of time from 5 to seconds, preferably 60 seconds. This step allows further absorption of the solution into the newly exposed surface and a resultant further dissolving of fresh plastic in such surface. However, most significantly, this optional step allows the portion of the solution which the surface retains thereon, but does not actually absorb therein, and which solution contains the dissolved plastic, to disperse uniformly the dissolved plastic as a viscous coating over the surface to be refinished. This coating allows the development, in subsequent steps of the process, of a high gloss refinished surface that is extremely uniform in texture and appearance.

Upon completion of the spraying operation or upon completion of the optional step if it is utilized, the article will have a certain amount of solution which contains the dissolved plastic, coating the surface to be refinished.

To effect a volatilization of the solution containing the dissolved plastic, whereby such plastic is redeposited on the surfaces to refinish the same, the article, after either the spraying operation or the optional step, is subjected to an initial drying operation for a period of 30 to 600 seconds, preferably 120 seconds. The drying'medium is air heated to a temperature in the range of 95 to 140 F., preferably 100 to 105 F. This drying operation removes from the newly refinished, high gloss surface of the article any unabsorbed solution containing dissolved plastic which remains thereon after having been exposed to either the spraying operation or the latter followed by exposure to the substantially saturated atmosphere. As this portion of the solution is removed from the surface by volatilization thereof, the plastic contained therein is redeposited on the surface to refinish the same to the gloss characteristics of the plastic obtained in the initial molding thereof.

This initial drying operation is also effective to partially remove some of the solution which has been entrapped by the plastic. However, it has been found that the plastic redeposited to form the refinished surface tends to solidify into a structure which is substantially impervious to the rapid passage of solution therethrough. Therefore, a quantity of the entrapped solution cannot be removed by the initial drying operation. This entrapped solution may, however, escape through such a solidified surface over a prolonged period of time.

Placing the article in the aforementioned stream of heated air also eliminates any tendency for moisture to condense on the newly developed surface while the plastic is being redeposited thereon. If moisture were allowed to condense on such a surface, at this time, it could result in a surface exhibiting a dull, whitish appearance, commonly known as blushing.

In the initial development of the method of this invention, the process was terminated by allowing the articles, after subjection to the initial drying operation, to dry at an ambient temperature for a period of time sufficient to permit handling of such articles without adversely affecting the newly developed surface thereon. It was felt that the solution entrapped below the newly developed surfaces would escape over a prolonged period of time with no detrimental effect to such a surface. However, it was found that articles having newly developed, high gloss surfaces finished only to this point were unsatisfactory when tested under normal use conditions, as such surfaces deteriorated within a relatively short time.

Extensive testing and detailed examination of these latter articles established that the surfaces exhibited a high state of stress when refinished only to this point. Such stresses are generally of a temporary nature and cause no difficulty. However, 'in this instance testing showed that the high degree of stress buildup in this plastic material was not of a temporary nature as anticipated. Rather, the stress remained in its high state even after prolonged periods of drying at an ambient temperature. Such stress buildup is apparently occasioned by an interaction between the removal of the remaining entrapped solution from the refinished surface, which results in shrinkage, and the increasing rigidity of such a surface as the solution is removed therefrom,

When such highly stressed articles were tested under normal use conditions, a resulting breakdown of the surfaces of the plastic material occurred in two distinct ways:

in one, the surfaces were easily stress cracked; in another, caused by the too rapid escape of entrapped solution as the surfaces were degenerated by appearance of so-called craters over the refinished surfaces.

It is believed that the cracking of a highly stressed surface results from the contact of such a surface with certain foreign contaminants such as human perspiration, tobacco smoke, cosmetics and the like, which contaminants are believed to be stress cracking agents. If this is actually true, it would at least partially explain why the contact of such contaminants with a highly stressed surface would relieve such stresses through the formation of minute surface cracks in the plastic. The components in the contaminants of perspiration, smoke, cosmetics and the like would then have an ample opportunity to penetrate easily into the minutely cracked surface and thereby give rise to the rapid discoloration of the newly developed surface.

The formation of small craters throughout the refinished surface was a completely unexpected phenomena. The surface cratering defect starts out as a small pinhole in the surface of the plastic which gradually grows over a period of days or weeks to give the appearance of a crater. Many craters in the same area of the refinished surface gives such a surface an appearance similar to the lunar surface. While no absolute theoretical explanation of this phenomena is known at the present time, it appears that the cratering is effected through a localized loss of diluent from the surface which results from the attacking of such surface by the aforementioned foreign contaminants at specific sites on the surface such as scratches or by foreign material embedded in the surface.

In view of the aforementioned problems in relation to stress cracking and cratering of newly developed surfaces on such articles, it was thought that a prolonged initial drying period would sufiice to eliminate such problems. However, articles processed by extending the initial drylng period for time lengths in excess of that prescribed above were also found to fail in the above-described manner when they were tested under normal conditions. More specifically, after a prolonged initial drying period at an elevated temperature, the article still had newly developed surfaces thereon which, under normal use conditions, were susceptible to stress cracking and cratering defects.

Upon further extensive investigation it was determined not only that articles made of an acrylonitrile-butadienestyrene copoly mer must be subjected to the initial drying operation as outlined above, but also that the refinished surfaces thereof must be maintained in a suitable drying environment at moderate temperatures for a period of time to allow purposely a substantial development of the stress forces to occur therein that are occasioned by removal therefrom of the entrapped solution. Thereafter, the articles must again be heated to a higher temperature such that the stress forces developed therein may be relieved.

While many drying environments, which can be main tained at a moderate temperature, may be utilized with the method of this invention, the most economical drying environment that may be utilized is a simple room drying operation. This room drying operation may be carried out in ambient air for a period from 5 to 48 hours, preferably 16 hours. Moreover, it was found that the development of stress forces from the 16th to the 48th hour is relatively minor and almost complete development of stress forces is achieved by the 24th hour. No beneficial result was found by holding the articles in ambient air in excess of 48 hours.

If a moderate drying environment is utilized wherein air is heated to a temperature of to F., a reduction in the drying time is realized in that a substantial development of stress forces in the surface of the article is achieved in a shorter period of time. However, for the moderate drying environment, the temperature should not be allowed to rise too high. Otherwise, the refinished surface will develop a whitish, hazy appearance commonly called bloom. It is believed that the hazy appearance is a result of rapid heating.

After the period of drying of the article in a moderate environment, during which a substantial development of the stress forces occur in the refinished surface of an article made of ABS type plastic, the article must be subjected to a heating operation in order to obtain the benefits of the method of this invention. This heating operation involves a heating period of 30 to 180 minutes, preferably 60 to 120 minutes, in air maintained at a temperature in the range of 140 to 225 F. Although the full heating period may be carried out at a single temperature in the given range, preferably the first 15 minutes of heating is at 140 F. and the balance thereof is at 170 to 175 F. This heating operation has been found very effective both to relieve all the stresses developed in the refinished surface and to remove virtually all remaining solution which would eventually escape spontaneously from the plastic. The removal of such solution insures that further development of stresses in the refinished surfaces after such surfaces have been returned to ambient temperature is substantially eliminated.

Thus, it may be seen that in order to insure the development of stress-free surfaces in the refinishing of articles made from acrylonitrile-butadiene-styrene copolymer it is necessary to allow the refinished material to be held at a moderate temperature in a drying environment for a period of time sufficient to allow development of stress forces therein, with these stress forces later being relieved by a heat treating operation.

When the stresses are so relieved, it was found that the refinished article surface not only had excellent gloss characteristics, but also physical characteristics comparable to thoses found on the surfaces developed in the initial molding of the copolymer. The refinished surfaces, although attackable by the same materials which attack an originally molded surface, still have the use period expectancy in telephone installations which compare to newly molded articles, and a use expectancy far exceeding that obtained from articles having highly stressed refinished surfaces.

When the two-stage permeating agent of 5 by volume of dichloromethane and 50% by volume of 1,1,1-trichloroethane is used with the method of this invention, slight adjustments are made to the temperatures and time lengths of some of the steps in the method. The times and temperatures utilized with this solution will be set forth hereinbelow as a second example of the method of this invention.

The spraying operation of the solution of 50% by volume of dichloromethane and 50% by volume 1,1,l-tricloroethane may be carried out for a period of to 40 seconds, preferably to 20 seconds, with the temperature of the solution being maintained at 60 to 90 F., preferably 70 to 80 F.

If the sprayed article is subjected to the optional step of being maintained in the substantially saturated atmosphere of the vapors of the solution, the period of time therefore is 5 to L20 seconds, preferably 90 seconds.

The initial drying operation utilized with the dichloromethane-1,1,l-trichloroethane solution is from 30 to 600 seconds, preferably 120 seconds at a temperature in the range of 105 to 150 F., preferably 105 to 110 F.

The suitable drying environment, used either after the spraying operation or the optional step, may be the same as employed in the first example of the method of this invention.

The heating operation is then carried out for a period of time from 10 to 180 minutes, preferably 60 to 120 minutes, in air maintained at a temperature in the range of 140 to 225 F., preferably 150 to 160 F.

There has been disclosed herein a method, with two specific examples given, for refinishing marred, scratched, minutely cracked and stained surfaces of articles made from a copolymer of the acrylonitrile-butadiene-styrene type which is simple and effective in operation and economical to utilize. The method produces new surfaces on such articles having both physical characteristics and gloss characteristics comparable to those obtained on the surfaces of such articles in the initial molding thereof. Moreover, the method may be utilized to refinish the most complex surfaces found on articles molded from such a copolymer. The method also allows for repeated surface refinishing of articles, such as telephone housings, handles, and end caps made from acrylonitrile-butadiene-styrene copolymer, to the appearance and physical characteristics obtained in the initial molding of the article.

While preferred methods of this invention have been disclosed, many modifications thereof will be apparent to one skilled in the art, and it is intended that the invention as claimed be interpreted as including all modifications which fall within the true spirit and inventive scope thereof.

What is claimed is:

1. A method of refinishing the surface of a plastic article made from an acrylonitrile-butadiene-styrene copolymer which comprises the steps of:

contacting the surface of the plastic article to be refinished With a two-stage permeating agent, a quantity of said agent, in the first stage, penetrating into the surface to a depth effective to cause a removal therefrom of an outer oxidized layer of plastic so that a new surface is uncovered and another quantity of said agent, in the second stage, being absorbed into said uncovered surface to a depth effective to cause a dissolving of a portion of said uncovered surface so that a portion of said agent coating said surface contains dissolved plastic;

drying the article for a time sufiicient both to allow an evaporation of said agent coating said surface and a redeposition of said dissolved plastic on said surface to cause a refinishing thereof and to allow a substantial development of stress forces to be achieved in said refinished surface as a portion of said agent absorbed therein is removed therefrom; and

heating the article to a temperature below the melting point of the plastic for a period of time sufiicient both to relieve the stresses developed in said refinished surface and to remove virtually all of the remaining of said absorbed agent therefrom.

2. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer which comprises the steps of:

contacting the surfaces of the plastic article to be refinished with a two-stage permeating agent, a quantity of said agent, in the first stage, penetrating into such surfaces to a depth effective to cause a removal therefrom of an outer oxidized layer of plastic so that new surfaces are uncovered and another quantity of said agent, in the second stage, being absorbed into said uncovered surfaces to a depth effective to cause a dissolving of a portion of said uncovered surfaces so that a portion of said agent coating said surfaces contains dissolved plastic;

initially drying the article in a heated environment both to allow a volatilization of said agent coating said surfaces and a simultaneous redeposition of said dissolved plastic on said surfaces to cause a refinishing thereof and to eliminate the condensation of moisture on said refinished surfaces while said agent is being volatilized therefrom;

drying the article in a moderate environment for a further period of time sufficient to evaporate a substantial portion of the agent absorbed in said surfaces so that a substantial development of stress forces is achieved in said refinished surfaces; and

heating the article to a temperature below the melting point of the plastic for a period of time sufficient both to relieve the stresses developed in said refinished surfaces and to remove virtually all of said remaining absorbed agent therefrom.

3. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer which comprises the steps of:

contacting the surfaces of the plastic article to be refinished with a two-stage permeating agent, a quantity of said agent, in the first stage, penetrating into such surfaces to a depth effective to cause a removal therefrom of an outer oxidized layer of plastic so that new surfaces are uncovered and another quantity of said agent, in the second stage, being absorbed into said uncovered surfaces to a depth effective to cause a dissolving of a portion of said uncovered surfaces so that a portion of said agent coating said surfaces contains dissolved plastic;

maintaining the article in a substantialy saturated atmosphere of the vapors of said agent for a time sufficient to allow said portion of said agent coating said surfaces to have a uniform concentration of dissolved plastic therethrough;

initially drying the article in a heated environment both to allow a volatilization of said agent coating said surface and a simultaneous redeposition of said dissolved plastic on said surfaces to cause a refinishing thereof and to eliminate the condensation of moisture on said refinished surfaces while said agent is being volatilized therefrom;

drying the article in a moderate environment for a further period of time sufficient to evaporate a substantial portion of the agent absorbed in said surfaces so that a substantial development of stress forces is achieved in said refinished surfaces; and

heating the article to a temperature below the melting point of the plastic for a period of time suflicient both to relieve the stresses developed in said refinished surfaces and to remove virtually all of said remaining absorbed agent therefrom.

4. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer as defined in claim 2 wherein said two-stage permeating agent consists essentially of 65 to 100% by volume of dichloromethane and 35 to by volume of trichlorotrifluoroethane.

5. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer as defined in claim 3 wherein said two-stage permeating agent consists essentially of 65 to 100% by volume of dichloromethane and 35 to 0% by volume of trichlorotrifluoroethane.

6L A method of refinishing surfaces of a plastic article made from an aerylonitrile-butadiene-styrene copolymer as defined in claim 2 wherein said two-stage permeating agent consists essentially of 6-5 to 100% by volume of dichloromethane and 35 to 0% by volume of tricholortrifluoroethane, wherein:

said contacting operation is a spraying operation carried out for a period of to 40 seconds, with the temperature of said agent maintained at a temperature of 40- to 90 F., wherein;

said initial drying operation is for a period of 30 to 600 seconds in air heated to a temperature in the range of 95 to 140 F., wherein;

said moderate drying operation is for a period of 5 to 48 hours in air maintained at ambient temperatures, and wherein;

said heating operation is for a period of 30 to 180 minutes in air maintained at a temperature in the range of 140 to 225 F.

7. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butaidene-styrene copolymer as defined in claim 3 wherein said two-stage permeating agent consists esesntially of 65 to 100% by volume of dichloromethane and 35 to 0% by volume of trichlorotrifluoroethane, wherein:

said contacting operation is a spraying operation carried out fo ra period of 5 to 40 seconds, with the temperature of said agent maintained at a temperature of 40 to F., wherein;

said article is maintained in said saturated atmosphere of the vapors of said agent for a period of time from 5 to 120 seconds, wherein;

said initial drying operation is for a period of 30 to 600 seconds in air heated to a temperature in the range of to 140 F., wherein;

said moderate drying operation is for a period of 5 to 48 hours in air maintained at ambient temperatures, and wherein;

said heating operation is for a period of 30 to 180 minutes in air maintained at a temperature in the range of 140 to 225 F.

8. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer as defined in claim 2 wherein said two-stage permeating agent consists essentially of 70% by volume of dichloromethane and 30% by volume of trichlorotrifluoroethane, wherein:

said contacting operation is a spraying operation carried out for a period of 10 to 20 seconds, with the temperature of said agent maintained at a temperature of 60 to 70 F., wherein;

said initial drying operation is for a period of 120 seconds in air heated to a temperature in the range of to F., wherein;

said moderate drying operation is for a period of 16 hours in air maintained at ambient temperatures, and wherein;

said heating operation is for a period of 60 to minutes in air maintained at a temperature of F. for the first 15 minutes and thereafter at a temperature in the range of to F.

9. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer as defined in claim 3 wherein said two-stage permeating agent consists essentially of 7 0% by volume of dichloromethane and 30% by volume of trichlorotrifluoroethane, wherein:

said contacting operation is a spraying operation carried out for a period of 10 to 20 seconds, with the temperature of said agent maintained at a temperature of 60 to 70 F., wherein;

said article is maintained in said saturated atmosphere of the vapors of said agent for a period of 60 seconds, wherein; said initial drying operation is for a period of 120 seconds in air heated to a temperature in the range of 100 to 105 F., wherein;

said moderate drying operation is for a period of 16 hours in air maintained at ambient temperatures, and wherein;

said heating operation is for a period of 60 to 120 minutes in air maintained at a temperature of 140 F., for the first 15 minutes and thereafter at a temperature in the range of 170 to 175 F.

10. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer as defined in claim 2 wherein said two-stage permeating agent consists essentially of 40 to 100% by volume of dichloromethane and 60 to 0% by volume of 1,1,l-trichloroethane.

11. A method of refinishing surfaces of a .plastic article made from an acrylonitrile-butadiene-styrene copolymer as defined in claim 3 wherein said two-stage permeating agent consists essentially of 40 to 100% by volume of dichloromethane and 60 to 0% by volume of 1,1,1-trichloroethane.

12. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer as defined in claim 2 wherein said two-stage permeating agent consists essentially of 40 to 100% by volume of dichloromethane and 60 to by volume of 1,1,1-trichloroethane, wherein:

said contacting operation is a spraying operation carried out for a period of to 40 seconds, with the temperature of said agent maintained at a temperature of 60 to 90 F., wherein;

said initial drying operation is for a period of 30 to 600 seconds in air heated to a temperature in the range of 105 to 150 F., wherein;

said moderate drying operation is for a period of 5 to 48 hours in air maintained at ambient temperatures, and wherein;

said heating operation is for a period of to 180 minutes in air maintained at a temperature in the range of 140 to 225 F.

13. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer as defined in claim 3 wherein said two-stage permeating agent consists essentally of 40 to 100% by volume of dichloromethane and 60 to 0% by volume of 1,1,1-trichloroethane, wherein:

said contacting Operation is a spraying operation carried out for a period of 5 to 40 seconds, with the temperature of said agent maintained at a temperature of 60 to 90 F., wherein; said article is maintained in said saturated atmosphere of the vapors of said agent for a period of time from 5 to 120 seconds, wherein;

said initial drying operation is for a period of 30 to 600 seconds in air heated to a temperature in the range of 105 to 150 F., wherein;

said moderate drying operation is for a period of 5 to 48 hours in air maintained at ambient temperatures, and wherein;

said heating operation is for a period of 10 to 180 minutes in air maintained at a temperature in the range of 140 to 225 F.

14. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer as defined in claim 2 wherein said two-stage permeating agent consists essentially of 50% by volume of dichloromethane and 50% by volume of 1,1,1-trichloroethane, wherein:

said contacting operation is a spraying operation carried out for a period of 10 to 20 seconds, with the temperature of said agent maintained at a temperature of 70 to 80 F., wherein; said initial drying operation is for a period of 120 seconds in air heated to a temperature in the range of 105 to 110 F., wherein;

said moderate drying operation is for a period of 16 hours in air maintained at ambient temperatures, and wherein;

said heating operation is for a period of 30 minutes in air maintained at a temperature in the range of 150 to 160 F. 15. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer which comprises the steps of:

spraying the surfaces of the plastic article to be finished for a period of 10 to 20 seconds with a two-stage permeating agent consisting essentially of 50% by volume dichloromethane and 50% by volume 1,1,1- trichloroethane, with the temperature of said agent maintained at to F.

maintaining the article in a substantially saturated atmosphere of the vapors of said agent for a period of seconds;

initially drying the article for a period of 120 seconds in air heated to a temperature in the range of to F.;

drying the article for a period of 16 hours in air maintained at ambient temperature, and;

heating the article for a period of 30 minutes in air maintained at a temperature in the range of F. 16. A method of refinishing surfaces of a plastic article made from an acrylonitrile-butadiene-styrene copolymer and having a permeable outer oxidized layer of plastic, which comprises the steps of:

permeating the oxidized layer with a solvent for the plastic for a sufficient period of time to remove the oxidized layer by dissolving a portion of the underlying plastic, and to absorb a quantity of the now dissolved plastic containing solvent into the surfaces of the newly exposed plastic; drying the article by first passing thereover air heated to a temperature of 90140 F., for a period of 30 to 600 seconds, and then passing thereover air maintained at ambient temperature for a period of 5 to 48 hours; and then heating the article to a temperature below the melting point of the plastic for a period of time sufficient to remove all the absorbed solvent from the surfaces thereof and to relieve any stress forces developed therein.

References Cited UNITED STATES PATENTS 2,651,811 9/1953 Coney 264-341 3,020,661 2/1962 Miller et al. 264341 3,332,881 7/1967 Burt et al 252161 JACOB H. STEINBERG, Primary Examiner.

U.S. Cl. X.R. 

